A solid laser, semiconductor laser and gas laser having a large output and a small size, which radiate an ultraviolet ray, visible light or infrared ray having a wavelength from 300 to 1,200 nm, have become easily available, and these lasers are very useful for recording light sources used in the direct plate making based on digital data, for example, from a computer. Various investigations on recording materials sensitive to such various laser beams have been made. Typical examples thereof include firstly recording materials capable of being recorded with an infrared laser having an image-recording wavelength of 760 nm or longer, for example, a positive type recording material described in U.S. Pat. No. 4,708,925, an acid catalyst crosslinking type negative type recording material described in JP-A-8-276558 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and a radical polymerization type negative type recording material containing an infrared absorbing agent described in JP-A-2009-91555. Secondly, as recording materials responsive to an ultraviolet ray or visible light laser having a wavelength from 300 to 700 nm, many radical polymerization type negative type recording materials, for example, those described in U.S. Pat. No. 2,850,445 and JP-B-44-20189 (the term “JP-B” as used herein means an “examined Japanese patent publication”) are known.
Further, with respect to hitherto known lithographic printing plate precursors (hereinafter, also referred to as PS plates), after image exposure a process of removing the non-image area by dissolution (development processing) is indispensable and a post-processing process, for example, washing the printing plate after the development processing with water, treatment of the printing plate after the development processing with a rinse solution containing a surfactant or treatment of the printing plate after the development processing with an oil-desensitizing solution containing gum arabic or a starch derivative, is also necessary. The point that such additional wet treatments are indispensable is a large subject of investigation in hitherto known PS plates. Even when the first half (image-forming processing) of plate making process is simplified by the above-described digital processing, the effects due to the simplification is still insufficient as long as the last half (development processing) is the troublesome wet treatment.
Particularly, the consideration for global environment has become a great concern throughout the field of industry in recent years. In view of the consideration for global environment, a treatment with a developer closer to a neutral range and a small amount of waste liquid are subjects of further investigations. In addition, it is desirable that the wet type post-processing is simplified or changed to a dry type processing.
From this viewpoint, as one method for simplifying the processing process, a method of one bath processing wherein development and a gum solution treatment are simultaneously conducted is known. Specifically, the method is a simple development process which does not require a post-water washing process and in which after image exposure, a lithographic printing plate precursor is subjected without undergoing a pre-water washing process to removal of a protective layer, removal of a non-image area and a gum solution treatment simultaneously with one bath and then drying without undergoing a post-water washing process to perform a printing process.
As another method of omitting the processing process, a method referred to as on-press development wherein an exposed lithographic printing plate precursor is mounted on a cylinder of a printing machine and the non-image area of the lithographic printing plate precursor is removed by supplying dampening water and ink while rotating the cylinder is known. Specifically, according to the method, the lithographic printing plate precursor is exposed imagewise and then mounted on a printing machine as it is to complete development processing in a conventional process of printing.
In any lithographic printing plate precursor of conventional development process, simple development process and on-press development process, the common problem of lithographic printing plate precursor having a hydrophilic protective layer is deterioration of ink receptivity. It is believed that this is caused by a hydrophilic component in the protective layer which gets into the image-recording layer and the image-recording layer is cured as it is by exposure to from the image area. This problem is particularly notable in the case where hydrophobicity of the image-recording layer is not sufficient.
It is proposed to incorporate a cellulose into a protective layer in order to impart ink receptivity in Japanese Patent 4162365 or JP-A-2008-162056. However, the technique is insufficient in view of balance between the ink receptivity or printing durability and the development property.
Further, a lithographic printing plate precursor having provided on a support, an image-recording layer capable of being removed with either printing ink, dampening water or both of them containing an actinic radiation absorber, a polymerization initiator and a polymerizable compound and a protective layer containing an inorganic stratiform compound in this order is described in JP-A-2005-119273. However, the technique has a problem in that the inorganic stratiform compound having a hydrophilic surface and a polyvinyl alcohol resin which is used as a binder get into the image-recording layer during the coating and drying stages and the image-recording layer is cured as it is by exposure to from the image area so that the ink receptivity just after the preparation and after the preservation of lithographic printing plate precursor is deteriorated.